Additives to suppress silica scale build-up

ABSTRACT

Composition comprising a plurality of particulates wherein at least some particulates are at least partially covered with a coating that impedes the intrusion of water into the particulates; and, a silica scale control additive, wherein the silica scale control additive is capable of suppressing silica scale build-up proximate the plurality of particulates. Some compositions further include a treatment fluid wherein and the silica scale control additive are present in the treatment fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. Nos. 61/104,610, 61/104,620, 61/104,624, and 61/104,629, each filedOct. 10, 2008.

This application is related to U.S. patent application Ser. No.12/573,999 (U.S. Patent Application Publication 2010/0089578), entitled“Prevention of Water Intrusion into Particulates,” by Nguyen et al.,U.S. patent application Ser. No. 12/574,018 (U.S. Patent ApplicationPublication 2010/0093566), entitled “Ceramic Coated Particulates,” byReyes et al., and U.S. patent application Ser. No. 12/574,054 (U.S.Patent Application Publication 2011/0253374), entitled “GeochemicalControl of Fracturing Fluids,” by Reyes et al., filed on Oct. 6, 2009,which are hereby incorporated by reference in their entirety.

BACKGROUND

The present disclosure relates to treatments and compounds useful insubterranean formations, and, at least in some embodiments, totreatments and compounds wherein particulates and/or surfaces may besubject to silica scale build-up.

In the production of fluids, such as hydrocarbons or water, from asubterranean formation, the subterranean formation should besufficiently conductive to permit the flow of desirable fluids to a wellbore penetrating the formation. Among others, hydraulic fracturing maybe a useful treatment for increasing the conductivity of a subterraneanformation. Hydraulic fracturing operations generally may involve pumpinga treatment fluid (e.g., a fracturing fluid or a “pad fluid”) into awell bore that penetrates a subterranean formation at a sufficienthydraulic pressure to create or enhance one or more pathways, or“fractures,” in the subterranean formation. Enhancing a fracturegenerally involves extending or enlarging a natural or pre-existingfracture in the formation. These fractures generally increase thepermeability of that portion of the formation. The treatment fluid maycomprise particulates, including proppant particulates that aredeposited in the resultant fractures. The particulates are thought tohelp prevent the fractures from fully closing upon release of thehydraulic pressure, forming conductive channels through which fluid mayflow between the formation and the well bore.

It is generally believed that the surfaces of particulates generallycomprise minerals, which may react with other substances (e.g., water,minerals, treatment fluids, and the like) that reside in thesubterranean formation in chemical reactions caused, at least in part,by conditions created by mechanical stresses on those minerals (e.g.,fracturing of the mineral surfaces or the compaction of particulates).These reactions are herein referred to as “stress-activated reactions”or “stress-activated reactivity.” One type of these stress-activatedreactions may be diageneous reactions. As used herein, the terms“diageneous reactions,” “diageneous reactivity,” and “diagenesis”include chemical and/or physical processes that, in the presence ofwater, move a portion of the mineral in a particulate and/or convert aportion of the mineral in a particulate into some other form. A mineralthat has been so moved or converted is herein referred to as a“diageneous product” or “diagenic product.” Any particulate comprising amineral may be susceptible to these diageneous reactions, includingnatural silicate minerals (e.g., quartz), man-made silicates and glassmaterials, metal oxide minerals (both natural and man-made), and thelike.

Two of the principal mechanisms that diagenesis reactions are thought toinvolve are “pressure dissolution” and “precipitation processes.” Wheretwo water-wetted mineral surfaces are in contact with each other at apoint under strain, the localized mineral solubility near that point mayincrease, causing the minerals to dissolve. Minerals in solution maydiffuse through the water film outside of the region where the mineralsurfaces are in contact (e.g., the pore spaces of a particulate pack),where they may precipitate out of solution. The dissolution andprecipitation of minerals in the course of these reactions may reducethe conductivity of a particulate pack, inter alia, by clogging the porespaces in the particulate pack with mineral precipitate and/orcollapsing the pore spaces by dissolving solid mineral in the “walls” ofthose pore spaces. In other instances, minerals on the surface of aparticulate may exhibit a tendency to react with substances in thereservoir, formation, and/or treatment fluids that are in contact withthe particulates, such as water, gelling agents (e.g., polysaccharides,biopolymers, etc.), and other substances commonly found in these fluids.Molecules from such substances may become anchored to the mineralsurface of the particulate. These types of reactivity may furtherdecrease the conductivity of a subterranean formation, inter alia,through the obstruction of conductive fractures in the formation by anymolecules that have become anchored to the particulates resident withinthose fractures. Both types of reactions may generally require thepresence of a fluid, such as water, to occur to any significant extent.

Silica (silicon dioxide) appears naturally in a number of crystallineand amorphous forms, all of which are sparingly soluble in water; thusleading to the formation of undesirable deposits. Silicates can be saltsderived from silica or the silicic acids, especially orthosilicates andmetasilicates, which may combine to form polysilicates. Silicasolubility depends on, but not exclusively, a number of factors such aspH, temperature, and ionic composition. Most silicates, except thealkali silicates, are sparingly soluble in water. A number of differentforms of silica and silicate salt deposits are possible, and formationof deposits depends, among other factors, on the temperature and pH ofthe water.

SUMMARY

The present disclosure relates to treatments and compounds useful insubterranean formations, and, at least in some embodiments, totreatments and compounds wherein particulates and/or surfaces may besubject to silica scale build-up.

One embodiment of the present invention provides a method. The methodcomprises providing a silica scale control additive in a subterraneanformation. The method further comprises providing a particulate pack inthe subterranean formation. The method further comprises allowing thesilica scale control additive to suppress silica scale build-upproximate the particulate pack.

Another embodiment of the invention provides another method. The methodcomprises providing a fluid comprising a carrier fluid, a plurality ofparticulates, and a silica scale control additive. The method furthercomprises introducing the fluid into a subterranean formation. Themethod further comprises allowing at least some of the particulates toform a particulate pack in the subterranean formation. The methodfurther comprises allowing the silica scale control additive to suppresssilica scale build-up proximate the particulate pack.

Yet another embodiment of the invention provides a composition. Thecomposition comprises a plurality of particulates a silica scale controladditive, wherein the silica scale control additive is capable ofsuppressing silica scale build-up proximate the particulate pack.

The features and advantages of the present invention will be apparent tothose skilled in the art. While numerous changes may be made by thoseskilled in the art, such changes are within the spirit of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present disclosure relates to treatments and compounds useful insubterranean formations, and, at least in some embodiments, totreatments and compounds wherein particulates and/or surfaces may besubject to silica scale build-up.

The term “coating” as used herein refers to at least a partial coatingof some or all of the particulates. Neither complete nor substantialcoverage of the particulates or mix of particulates is implied by theterm “coating.” Rather, a particulate may be coated if it has, forexample, at least a partial coating.

The term “derivative” is defined herein to include any compound that ismade from one of the listed compounds, for example, by replacing oneatom in the listed compound with another atom or group of atoms,rearranging two or more atoms in the listed compound, ionizing one ofthe listed compounds, or creating a salt of one of the listed compounds.A derivative of a material may include, but is not limited to, acompound composition based on a plurality of base materials, a compositematerial, or an aggregated material of various compositions.

As used herein, the terms “diageneous reactions,” “diageneousreactivity,” and “diagenesis” include chemical and physical processesthat, in the presence of water, move a mineral and/or convert a mineralinto some other form. Examples of such minerals include, but are notlimited to, oxides or hydroxides of zirconium, magnesium, aluminum,titanium, calcium, strontium, barium, radium, zinc, cadmium, boron,gallium, iron, or any other element suitable for forming a diagenicproduct. Such minerals may be found in a particulate, in a formation,and/or introduced into a formation as “diagenesis source material.” Amineral that has been so moved or converted is herein referred to as a“diageneous product” or “diagenic product.”

As used herein, the term “aqueous fluid interaction” includes a varietyof possible interactions between an aqueous fluid and a particulate.Such interactions may include infiltration of the aqueous fluid into theparticulate, for example, by infiltrating pores, voids, crevices,cracks, and/or channels at or near the surface of the particulate. Suchinteractions may also include diagenesis.

As used herein, the term “diffusion barrier” includes any sort ofmaterial, including a coating, on or proximate to a particle thatimpedes and/or prevents aqueous fluid interaction with the particle. Forexample, some diffusion barriers fill or coat pores, voids, crevices,cracks, or channels at or near the particle's surface to impede and/orprevent infiltration by the aqueous fluid. As another example, somediffusion barriers impede and/or prevent diagensis.

As used herein, the term “diagenic protective materials” refers to oneor more diagenic products that may be selectively promoted in order toform a diffusion barrier.

As used herein, the term “filler” or “filler material” means aparticulate material that is capable of fitting within a pore, void,crevice, crack, or channel at or near the surface of a particulate or onsurfaces within the porous matrix of the individual particulates.

As used herein, the term “relatively low molecular weight” refers to amolecular weight that would encompass monomers and short-chain polymershaving physical dimensions from a few angstroms to several hundrednanometers.

As used herein, a “monolayer” refers to a coating of a materialapproximately one unit thick. For chemicals, this may mean a coating asthin as one molecule, and for particulate compositions, it may mean acoating one particulate grain deep.

As used herein, the terms “pores,” “voids,” “crevices,” “cracks,” and“channels” refer to features at or near the surface of a particulate.Any given particulate may have one or more pores, voids, crevices,cracks, or channels, or may be free of such features. One or more suchfeatures may be generally referred to as “surface features.” The use ofthe terms in conjunction is in no way intended to indicate that allthree must be present simultaneously, or at all, in order for theteachings of the present disclosure to apply.

As used herein, the terms “particle,” “particulate,” “proppantparticulate,” and “gravel” are all used to refer to either a singleparticle or a plurality of particles which may be used for supporting afracture in an underground formation, for forming a proppant pack, orfor use in forming a gravel pack. Such particles may be disposed in asubterranean formation, including in spaces in the rock itself,fractures within the rock, and/or a well bore penetrating thesubterranean formation.

As used herein, the term “pack” or “particulate pack” refers to acollection of particulates within an enclosed volume, wherein theparticulates may be juxtaposed and/or in contact with one another, andwherein pore spaces may be disposed between the particulates. Examplesof “packs” may include “proppant packs,” which may refer to a collectionof proppant particulates within a fracture, and/or “gravel packs,” whichmay refer to a grouping of particulates that are packed sufficientlyclose together so as to prevent the passage of certain materials throughthe pack.

The term “on-the-fly” is used herein to indicate that one flowing streamcomprising particulates is introduced into another flowing streamcomprising a hydrophobic coating agent so that the streams are combinedand mixed to flow as a single stream. In some instances, the streams maybe combined to flow as a single stream as part of an on-going treatmentat the job site. Such mixing can also be described as “real-time”mixing.

As used herein, the term “silica scale control additive” may be anyproduct capable of suppressing silica scale build-up by increasing thesolubility of silica in solution, inhibiting silica polymer chainpropagation, and/or decreasing the size or quantity of any silica scalecreated in a solution.

The term “gel,” as used herein and its derivatives refer to aviscoelastic or semi-solid, jelly-like state assumed by some colloidaldispersions.

If there is any conflict in the usages of a word or term in thisspecification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted for the purposes ofunderstanding this invention.

There are many advantages of the present invention, only some of whichare mentioned here. One advantage of the methods disclosed herein may bethe suppression of silica scale build-up within a particulate pack in asubterranean formation, including in the rock itself, fractures withinthe rock, and/or a well bore penetrating the subterranean formation.Without limiting the invention to a particular theory or mechanism, itis nonetheless currently believed that, when placed within a formation,a particulate pack may experience silica scale build-up due to silicondissolution from either the particulates or the formation. The siliconmay dissolve in fluids, such as formation fluids or treatment fluids.The dissolved silicon may then precipitate in various forms to createsilica scale within, upstream, or downstream of the particulate pack.Such silica scale may have a tendency to form or collect in theinterstitial spaces of the particulate pack, which may reduce thepermeability of the pack over time. As such, the suppression orinhibition of silicon dissolution and silica scale build-up may be ableto reduce the permeability loss in the particulate pack, therebyincreasing the ultimate productivity of the well.

Protecting particulates from such damage may be achieved in severalways. In an embodiment, a silica scale control additive may be utilizedto treat a particulate pack. The silica scale control additive maysuppress silica scale build-up by increasing the solubility of siliconwithin the particulate pack while simultaneously preventing largebuild-ups of silica scale. Various silica scale control additives may beused to limit the silica scale formation, as discussed in more detailbelow.

Protecting particulates from damaging interactions with aqueous fluidsmay be achieved in several ways. In accordance with embodiments of thepresent invention, these generally may include treating a particulatewith a diffusion barrier which acts to impede the particulateinteraction with aqueous fluids during and/or after placement in theformation. The diffusion barrier may comprise one of several types ofmaterials, including hydrophobic materials, diagenic protectivematerials, and various polymeric compositions. Some embodiments of thepresent invention may utilize filler material to fill the pores, voids,crevices, cracks, or channels that may be present in a particulatesurface. Alternatively, a filler material may be used to generate and/orplace the diffusion barrier. For example, a hydrophobic material may beused to coat a filler material, and the filler material may thengenerate a diffusion barrier (e.g., comprising a diageneous product) onthe particulates. The filler material may fill the pores, voids,crevices, cracks, or channels on the particulate surface, resulting in asurface that may be more hydrophobic than the original particulatesurface. Each of these materials and methods will be described in moredetail below.

The particulates that may be used in embodiments of the presentinvention include any proppant or gravel particulates that may be usedin a subterranean application. Suitable particulates may include sand,sintered bauxite, silica alumina, glass beads, etc. Other suitableparticulates include, but are not limited to, sand, bauxite, garnets,fumed silica, ceramic materials, glass materials, polymer materials,polytetrafluoroethylene materials, nut shell pieces, seed shell pieces,fruit pit pieces, wood, composite particulates, proppant particulates,degradable particulates, coated particulates, gravel, and combinationsthereof. Suitable composite materials may comprise a binder and aparticulate material wherein suitable particulate materials may includesilica, alumina, garnets, fumed carbon, carbon black, graphite, mica,titanium dioxide, meta-silicate, calcium silicate, kaolin, talc,zirconia, boron, fly ash, hollow glass microspheres, solid glass, andcombinations thereof. In certain embodiments, the particles may comprisecommon sand. In some embodiments, a derivative of one or more of theparticulate materials may also be used. Derivatives may includematerials such as compounds, composite materials, and aggregatedmaterials of various compositions. In some embodiments of the presentinvention, some or all of the particulates may be comprised of adiagenesis source material. In this embodiment, the particulates maycomprise oxides or hydroxides of zirconium, magnesium, aluminum,titanium, calcium, strontium, barium, radium, zinc, cadmium, boron,gallium, iron, or any other element suitable for forming a diagenicproduct. Suitable particulates may take any shape including, but notlimited to, the physical shape of platelets, shavings, flakes, ribbons,rods, strips, spheres, spheroids, ellipsoids, toroids, pellets, ortablets. Although a variety of particulate sizes may be useful in thepresent invention, in certain embodiments, particulate sizes may rangefrom about 200 mesh to about 8 mesh.

Embodiments of particulates of the present invention may contain pores,voids, crevices, cracks, or channels at or near the surface. Forexample, SEM micrographs at high magnification may show that thesurfaces of particles, such as particulates made from bauxite, may beladen with pores, voids, crevices, cracks, and channels. Without beinglimited by theory, it is believed that these pores, voids, crevices,cracks, or channels at or near the particulate surface may provide adirect path to allow a detrimental interaction between aqueous fluidsand the particles that may lead to degradation of the particles underformation pressure and temperature.

In some embodiments, the particulates may be treated or coated with oneor more suitable substances. Generally, the particulates may be treatedor coated with any substance which is suitable for traditionalparticulate treatments. In certain embodiments, the particulates may becoated so as to impede the intrusion of water into the particulates. Forexample, the particulates may be coated and/or used as discussed in“Prevention of Water Intrusion Into Particulates” by Nguyen et al., U.S.patent application Ser. No. 12/573,999 (U.S. Patent ApplicationPublication 20100089578); “Geochemical Control of Fracturing Fluids” byReyes et al., U.S. patent application Ser. No. 12/574,054 (U.S. PatentApplication Publication 20110253374); and/or “Ceramic CoatedParticulates” by Reyes et al., U.S. patent application Ser. No.12/574,018 (U.S. Patent Application Publication 20100093566), each filedon the same day herewith, and the entire disclosures of which are herebyincorporated by reference in their entirety. In an embodiment, a portionof the particulates may be coated so as to limit their diagenicreactivity while others may remain uncoated so as to provide a reactionsite for the diagenesis source material.

The particle compositions used in some of the embodiments of the presentinvention may comprise at least one particulate and a diffusion barrier,which may comprise a hydrophobic, or water repellant, material.Diffusion barriers may be initiated by and/or formed from a variety ofmaterials. For example, certain materials may initiate diffusionbarriers in some embodiments of the present invention. Suitablematerials may be any chemical agent capable of forming a hydrophobiccoating on the surface of particulates. In certain embodiments,particles comprising a diffusion barrier may have a retained strengthgreater than or equal to about 30%, as discussed in more detail below.In some embodiments, such diffusion barriers may enhance the recovery ofa reservoir, formation, and/or treatment fluid. In certain embodiments,a surfactant may be included in the coating material so as to improvethe coating process. Suitable coating materials may include oligomericmaterials, monomeric materials, oil-wetting compounds, and combinationsthereof to provide at least a monomolecular film, which may make themineral surfaces water-repellent or hydrophobic.

In one embodiment, a diffusion barrier may comprise the reactionproducts of a compound having a reactive silyl group. The diffusionbarrier may be formed by forming a silicon oxide layer or hybridorgano-silicon oxide anchor layer from a humidified reaction product ofsilicon tetrachloride or trichloromethysilane, followed by thevapor-deposition of a chloroalkylsilane. In another embodiment, thediffusion barrier may comprise a trimethylsilyl functional group. Forexample, if a fumed silica filler particle is used, the surface hydroxylgroups may be replaced with trimethylsilyl functional groups to form ahydrophobic filler particle. The diffusion barrier may also comprisesilicones or siloxanes. In an embodiment, the diffusion barrier maycomprise an organosilicon compound, which may include, for example, anorganosiloxane, an organosilane, a fluoro-organosiloxane, and afluoro-organosilane. The diffusion barrier may also comprise apolysiloxane or an organo-modified polysiloxane, which may include adi-betaine polysiloxane or a di-quaternary polysiloxane.

In another embodiment, a diffusion barrier may comprise polymers of afluoroalkyl-group containing silane compound, and the polymers mayinclude at least dimers and trimers of the silane compound. Thisdiffusion barrier may be made by preparing a solution, the solutionbeing produced by subjecting a fluoroalkyl-group contained silanecompound to a hydrolysis and a condensation polymerization to produce atleast dimers and trimers of the silane compound, coating the solutiononto the surface of the particulate or filler material, and heating thematerial to cause the fluoroalkyl group in the solution to be bonded tothe surface of the particulate solids so as to form a hydrophobic filmon the material. In another embodiment, the diffusion barrier maycomprise a fluoro-organosiloxane or a fluoro-organosilane compound,which may include, for example,2-(n-perfluoro-octyl)-ethyltriethoxysilane and perfluoro-octyldimethylchlorosilane.

In yet another embodiment, a diffusion barrier may comprise a polyamide.In still another embodiment, the diffusion barrier may comprise asilyl-modified polyamide.

In an embodiment, a diffusion barrier may comprisepolytetrafluoroethylene, plant oils, hydrocarbons, copolymerizedpolyvinylidene chloride, or any other substance capable of hindering orpreventing aqueous fluid penetration, permeation, or wetting of aparticulate.

In an embodiment, the particulates may be coated with a ceramic. Theceramic may impede aqueous fluid interactions between the particulatesand aqueous fluids, including aqueous treatment and/or formation fluids.In an embodiment, an appropriate ceramic may include silicon carbide,silicon nitride, boron carbon, boron carbide, diamond-like-carbon,titanium carbide, aluminum nitride, chromium carbide, mixed carbide,nitride, carbonitride alloys, and cubic boron nitride. In an embodiment,a plurality of ceramics may be used in conjunction to combineadvantageous effects. In an embodiment, a derivative of one or moreceramic materials may also be used. Derivatives may include materialssuch as compounds, composite materials, and aggregated compositions ofvarious ceramic materials.

One of ordinary skill in the art, with the benefit of this disclosure,will be able to determine which ceramic or ceramics should be coated ona particulate based on, for example, formation chemistry, formationconditions (e.g., temperature, pressure, etc.), particulate composition,resource availability, costs and logistics considerations, and anyphysical limitations inherent in the coating process. In an embodiment,the coating layer may vary in thickness depending on the subterraneanoperation requirements. In some embodiments, the ceramic may be amonolayer thick, while in other embodiments, a thicker layer may bedesired. In particular, some embodiments may provide a very thin ceramiclayer of subatomic thickness. In such embodiments, the ceramic thicknessmay be between about 100 nanometers and about 50,000 nanometers. Theresulting coated particulate may have ceramic from between about 0.1% toabout 10% by weight of the particulate. In another embodiment providinga ceramic layer of subatomic thickness, the ceramic thickness may bebetween about 100 nanometers and about 500 nanometers. The resultingcoated particulate may have ceramic from between about 0.5% to about 2%by weight of the particulate.

In some embodiments, a variety of methods may be useful in coating aceramic on particulates. Any method capable of coating a ceramic on aparticulate may be used. In an embodiment, chemical vapor deposition,physical vapor deposition, dip coating, spray pyrolysis, sputtering,sintering, and chemical vapor infiltration may be used to introduceceramic onto a particulate. For any methods requiring a chemicalreaction to form a ceramic coating (e.g., chemical vapor deposition orspray pyrolysis), any appropriate precursors may be determined by oneskilled in the arts. For example, single source precursors for formingsilicon carbides may include, but are not limited to, polycarbosilanes,polysilazanes, silylenes, perfluoroalkylsilanes or functionalizedsilylenes, and mixtures such as alkylchlorosilanes, ethylene, andhydrogen for instance. One skilled in the art will be able to determinethe appropriate coating technique, reaction conditions, and precursors,if needed, based upon the type of ceramic desired and the particulatecomposition. For embodiments in which more than one layer of the ceramicis coated on the particulates, the same or different coating methods maybe used. Due to the conditions generally required to form a ceramiccoating on a particulate, the particulates may generally be coated in amanufacturing process prior to being shipped to the well site. In someembodiments, the particulates may be coated at the well site and/oron-the-fly.

Certain methods of the present invention may result in a very thindiffusion barrier, comprising a protective material, a diagenic product,a treated filler material, or any combination thereof on a particulate.The use of relatively low molecular weight compounds in the coatingmethods may result in diffusion barriers as thin as a monolayer. Inanother embodiment, filler materials may act to produce a diffusionbarrier on a particulate less than about 10 micrometers thick. In analternative embodiment, the diffusion barrier may be less than about 1micrometer thick, or alternatively less than about 0.5 micrometersthick. Such thin coatings may effectively allow the coating of thepores, voids, crevices, cracks, or channels of the particulates. Thismay help to limit the particulate degradation due to interactions withaqueous fluids while preventing any detrimental interactions between theparticulates due to agglomeration of the particulate pack.

In another embodiment of the present invention, a method of initiating afluid barrier may comprise coating a filler particle with a protectivecoating, such as a hydrophobic material, and then mixing the coatedfiller particle with a particulate to form a diffusion barrier. Forexample, a fumed silica nano-particle may be treated such that surfacehydroxyl groups are replaced with trimethylsilyl functional groups toform a protective coating on the filler material. In this example, theparticulates may exhibit hydrophobic properties when mixed with thecoated filler material. For another example, the filler material may bea metallic compound capable of promoting the formation of diagenicproducts when placed in the formation. In this example, the particulatesmay be coated with filler material, and a diffusion barrier may beformed upon placement in the formation. In an embodiment, the fillermaterial may be a dry, free-flowing material suitable for mixing with aparticulate. The treated filler material may be mixed with theparticulates in an amount sufficient to impart a diffusion barrier tothe particulates. This may be an amount sufficient to partially coat theparticulates but not provide 100% coverage of each particle. In anembodiment, the treated filler material may be mixed with theparticulates in an amount ranging from about 0.025% to 50% by weight ofparticulates, or from about 0.25% to 50% by weight of particulates. Inan alternative embodiment, the treated filler material may be mixed withthe particulates in an amount ranging from about 0.25% to 5% by weightof particulates.

The filler material may comprise materials with particles ofmicrometer-size, sub-micrometer-size, nano-size, or a combinationthereof. The filler material may be reinforcing or non-reinforcing.Filler materials may include, for example, fumed silica, fused silica,garnet powder, clay, mica, alumina, finely divided quartz powder,amorphous silicas, meta-silicates, calcium silicates, calcine, kaoline,talc, zirconia, fly ash, boron, carbon black, fumed carbon, graphite,diamond, silicone carbide, aluminum hydrates, metal nitrides (such asboron nitride, and aluminum nitrides), metal oxides (such as aluminumoxide, zinc oxide, titanium dioxide or iron oxide), and any combinationthereof. In another embodiment, the filler material may comprise metalparticles, such as aluminum, zirconium, titanium, or derivativesthereof. In one embodiment, the average diameter of the filler materialparticles may be less than about 20 micrometers. In one embodiment, theaverage filler material particle diameter may range from about 0.05micrometers to about 10 micrometers, or from about 0.1 micrometers toabout 10 micrometers. In another embodiment, the particles of fillermaterial may have a size range of from about 0.1 micrometer to about 0.5micrometers, or from about 0.2 micrometers to about 0.5 micrometers.

In accordance with embodiments of the present invention, the fillermaterial particle size may be chosen, among other purposes, to achieve acoating of a particulate including the pore spaces on the particulatesurface. The choice of a filler material particle size may be based upona consideration of the surface characteristics of the particulate, whichmay be based on the choice of particulate material, crystal structure,and/or other characteristics. In an embodiment, the filler materialparticle size may be such that the maximum filler material particle sizemay be at least equal to, and, in some embodiments, less than, theexpected diameter of a pore, void, crevice, crack, or channel at or nearthe surface of the particulate. Consideration of any additional coatingthickness that the coating material may add to the filler material alsomay be a consideration in choosing a filler material having certainparticle sizes and shapes.

In an embodiment, a silica scale control additive may be used with aparticulate pack (e.g., a proppant or gravel pack) to suppress silicascale build-up by mitigating, inhibiting, or suppressing the formationand build-up of silica (also known as silica scale). Formation of silicascale may occur on the particulates, on the formation fracture face, orin a solution within a particulate pack. Silica scale control additivesmay increase the amount of soluble silica within a solution. Withoutintending to be limited by theory, it is believed that the silica scalecontrol additives inhibit the polymerization and build-up of silicicacid and colloidal silica by disrupting chain propagation. In anembodiment, a silica scale control additive may be any compound whichcontrols the formation of scale to some degree and does not negativelyreact with the particulates, the formation, a treatment fluid, aformation fluid, or any other aspect of the subterranean environment. Inan embodiment, suitable silica scale control additives may includepolyaminoamide dendrimers and polyethyleneimine, which may be combinedwith carboxymethylinulin and polyacrylates. In an alternativeembodiment, polyallylamines, copolymers of polyacrylamides, andpolyallyldiamethylammonium chloride may also be used as silica scalecontrol additives. Examples of suitable silica scale control additivesinclude ACUMER™ 5000 (a proprietary polymer having a molecular weight of5000 that is commercially available from Rohm and Hass of Philadelphia,Pa.); CLA-STA® XP (a water-soluble cationic oligomer oftrimethylamine-quaternized polyepichlorohydrin that preferentiallyadsorbs and replaces gel from clay and silica surfaces) and CLA-STA® FS(a polymer that stabilizes mineral fine particles by adsorbing onformation surfaces), each of which is available from Halliburton EnergyServices, Inc. of Duncan, Okla.

In some embodiments, a silica scale control additive may be added to atreatment fluid (e.g., a fracturing fluid, a carrier fluid, astimulation fluid, etc.) in an amount sufficient to suppress silicascale build-up by inhibiting the formation of silica scale. Thetreatment fluid may be aqueous, non-aqueous, or a combination of fluidtypes. Generally, the treatment fluid may comprise a carrier fluid,particulates, such as proppant, and one or more additives, such assilica scale control additives. In some embodiments, the amount ofsilica scale control additive may be any amount necessary to controlsilica and silicate deposition in the system being treated. In anembodiment, the amount may be any amount sufficient to obtain a retainedpermeability in a proppant pack of at least about 40%, the measurementof which is described in more detail below. In an embodiment, the amountof silica scale control additive may range from about 1 to about 1000parts per million (ppm) by weight of the carrier fluid. In analternative embodiment, the amount may range from about 1 to about 100ppm by weight of the carrier fluid. The pH of the carrier fluid may alsohave an impact on the effectiveness of the silica scale controladditive. In some embodiment, the pH of the carrier fluid may bemaintained at between about 4.0 and about 8.0. In an embodiment, the pHof the carrier fluid may be maintained between about 6.5 and about 7.5.

Silica scale control additives may be added to a well bore before,after, or during the placement of a particulate pack. In an embodiment,the silica scale control additive may be added to a fracturing fluid andcarried with the fracturing fluid during formation of the fractures. Inthis embodiment, the silica scale control additive may be in thefracturing fluid in the formation during the placement and setting of aparticulate pack. Alternatively, the silica scale control additive maybe mixed with a carrier fluid used to carry and set the particulate packin the formation. In still another embodiment, a silica scale controladditive may be utilized after a particulate pack has been placed in thewell bore. In such embodiments, a carrier fluid may be used to carry thesilica scale control additive into the well bore and through theparticulate pack. By way of example, a particulate pack may be contactedby a silica scale control additive. This technique also may be used as asubsequent treatment method to periodically treat the particulate packover time, among other purposes, in order to maintain permeability inthe particulate pack.

One embodiment of the present invention provides a method. The methodcomprises providing a silica scale control additive in a subterraneanformation. The method further comprises providing a particulate pack inthe subterranean formation. The method further comprises allowing thesilica scale control additive to suppress silica scale build-upproximate the particulate pack. In some embodiments, this method may beuseful in the recovery of fluids from the subterranean formation. Thefluids being recovered may be a fluid previously introduced into thesubterranean formation, an aqueous reservoir and/or formation fluid, ahydrocarbon fluid, or a combination thereof.

Another embodiment of the invention provides another method. The methodcomprises providing a fluid comprising a carrier fluid, a plurality ofparticulates, and a silica scale control additive. The method furthercomprises introducing the fluid into a subterranean formation. Themethod further comprises allowing at least some of the particulates toform a particulate pack in the subterranean formation. The methodfurther comprises allowing the silica scale control additive to suppresssilica scale build-up proximate the particulate pack. In someembodiments, this method may be useful in the recovery of fluids fromthe subterranean formation. The fluids being recovered may be a fluidpreviously introduced into the subterranean formation, an aqueousreservoir and/or formation fluid, a hydrocarbon fluid, or a combinationthereof.

Yet another embodiment of the invention provides a composition. Thecomposition comprises a plurality of particulates a silica scale controladditive, wherein the silica scale control additive is capable ofsuppressing silica scale build-up proximate the particulate pack. Insome embodiments, this method may be useful in preparation ofparticulates for subterranean treatments and/or usage of particulates insubterranean treatments.

In order to quantify the mechanical strength of the particulates andpermeability of the particulate pack, both before and after exposure toformation conditions and fluids, several test procedures may be utilizedto determine various particulate properties. The first test methodstudies temperature-promoted diagenesis of a particulate pack byexposing a particulate pack to a flowing solution of simulated formationfluid at an approximate formation temperature. The second procedurestudies stress/temperature-promoted diagenic growth through exposure ofa particulate pack to a static flow environment under simulatedformation pressures and temperatures. The mechanical strength ofindividual particulates may be measured before and after the testprocedures to determine the percentage of particulate strength lost dueto exposure to formation temperature or pressure. Alternatively, thepermeability of the particulate pack may be measured before and afterthe temperature-promoted diagenesis test in order to determine aretained permeability value for the particulate pack. As would beunderstood by one of ordinary skill in the art with the benefit of thisdisclosure, expected subterranean formation conditions (e.g.,temperature, pressure, formation fluid composition) for a selectedsubterranean formation will determine the appropriate formationconditions for test procedures.

In the temperature-promoted diagenesis test procedure, deionized watermay first be heated to a test temperature of between about 200 degreesFahrenheit (° F.) and about 600° F. by passing it through a heatexchanger coil. Simulated formation fluid may be formed by passing thedeionized water through multiple packs of crushed formation materialarranged in series. The number of formation packs required for the testmay vary such that the simulated formation fluid leaving the last packmay be in equilibrium with the crushed formation material. Throughexperimentation, the typical number of formation packs may generally bebetween about 1 and about 10. Crushed formation material may be screenedto remove fines and an approximately 8/35 mesh fraction may be used inthe formation packs.

In an embodiment, once a simulated formation fluid in equilibrium withthe crushed formation material is obtained, the simulated formationfluid may be directed to a column containing a particulate pack. Thetemperature in the particulate pack may be maintained at an approximateformation temperature between about 200° F. and about 600° F., whichapproximately corresponds to the temperature of the deionized waterfirst entering the system. A flow rate of simulated formation fluid maybe maintained at approximately 1 milliliter per minute during the test.

The flow test may be maintained for between about 10 to about 200 days,and in an embodiment, for at least about 20 days. After this time, theparticulate pack may be disassembled in order to test the mechanicalproperties of individual particles, as discussed in more detail below.For example, surface and compositional analysis may be made afterdisassembly to determine what types of materials are being formed underthe simulated formation conditions. A permeability test may also beperformed at this time. In this test, the permeability of theparticulate packs may be measured at room temperature prior disassemblyof the particulate pack. The measured permeability of the pack may thenbe compared with an initial permeability measurement made of the pack atroom temperature before the pack is placed in the testing apparatus.Comparing the initial permeability measurement with the permeabilitymeasurement obtained after the pack is subjected to the test conditionsmay allow for a retained permeability to be calculated.

The stress/temperature-promoted diagenesis test method may involve thetesting of the particulate pack under static flow conditions atapproximate formation pressures and temperatures. In this method, a packof particulates may be loaded in a test cell and filled with a saltsolution. The test cell may be loaded from between about 0.5 pounds persquare foot (lb/ft²) of particulates to about 3.0 lb/ft² ofparticulates. In an embodiment, an approximately 2% KCl solution may beused as the fluid medium. Formation wafers, either manufactured fromformation core material or from rock outcrop material, may be placedabove and below the particulate pack in the test column. The system maythen be shut in and placed under simulated formation pressure and heatedto approximate formation temperatures. In an embodiment of this method,the temperature may be maintained at between about 100° F. and about550° F. In another embodiment, the temperature may be maintained atbetween about 100° F. and about 350° F. The pressure may be maintainedat between about 2,000 psi and about 10,000 psi. In another embodiment,the pressure may be maintained at between about 5,000 psi and about8,000 psi. In an embodiment, the test may be conducted for between about1 to about 50 weeks, and in another embodiment, the test may beconducted for at least about 4 weeks (about 28 days).

Upon completion of the stress/temperature-promoted diagenesis test, thetest cell may be disassembled and the particulate pack removed fortesting. As with the flow test method, additional tests may also beperformed at this time. For example, surface and compositional analysismay be made after disassembly to determine what types of materials arebeing formed under the simulated formation conditions. Alternatively,the resulting interstitial fluid may be analyzed to determine therelative solubility of the particulates under formation conditions.

Changes in the mechanical properties of the particulates obtained fromeither the stress/temperature-promoted diagenesis test or thetemperature-promoted diagenesis test may be determined using asingle-grain crush-strength analysis. The analysis may utilize a Weibullstatistical analysis procedure based on a plurality of particulate crushsamples. The crush test may be based on a uni-axial compressive pointloading of a particle. Under a compressive loading in the uni-axialdirection, a spherical particle may be under tension in directionsperpendicular to the loading with a tensile stress, σ, calculated by

$\sigma = \frac{2.8F}{\pi\; d^{2}}$where d is the diameter of each particle and F is the load at failure.

A Weibull analysis may include a statistically significant number ofcrush samples, which may range from about 10 to about 50 individualcrush samples, or from about 20 to about 40 individual crush samples. Inan embodiment, a sample size of between about 25 and about 30 individualcrush samples of particulates may be used in the analysis. All of thestrength data points may then be sorted from low to high as σ₁<σ₂<σ₃<. .. <σ_(N), where N represents the total number of samples. A probabilityof failure may be calculated from the equation:

$P_{f} = ( \frac{\# - 0.5}{N} )$where, as before, N is the total number of samples, for example about 30samples, and # is the index number for the sorted strength values (e.g.,1 through N). A linear plot may be obtained by plotting

${\ln( {\ln( \frac{1}{1 - P_{f}} )} )}{vs}\;{\ln(\sigma)}$A Weibull distribution may be found by linear fitting and generating anequation:

${\ln( {\ln( \frac{1}{1 - P_{f}} )} )} = {m\;{\ln( \frac{\sigma}{\sigma_{0}} )}}$where m is the Weibull modulus and σ₀ is the characteristic strength.The strength will tend to increase along with the reliability of thestrength calculation when the σ₀ and m values increase. Thecharacteristic strength changes in the particulates may then bedetermined. By comparing the characteristic strength of the particulatesprior to exposure to the simulated formation fluid with thecharacteristic strength of the particulates after exposure to thesimulated formation fluid, a retained strength value may be calculatedfrom the equation:

$\sigma_{0{retained}} = ( \frac{\sigma_{0{exposed}}}{\sigma_{0{unexposed}}} )$where, σ_(0 exposed) is the characteristic strength of the particlesafter exposure to the simulated formation fluid, and σ_(0 unexposed) isthe characteristic strength of the particles prior to exposure.Similarly, a retained permeability may be calculated by dividing thepermeability measured at the end of the temperature-promoted diagenesistest with the permeability measured at the beginning.

In an embodiment, a single set of test conditions may be utilized forcomparison of different sets of sets of particles comprising diffusionbarriers and/or filler materials. The retained strength value is definedto be measured by the stress/temperature-promoted diagenesis test. Inthis method, a pack of particulates is loaded in a test column andfilled with a salt solution comprising an approximately 2% KCl solution.The test cell is loaded with about 2 lb/ft² of particulates. Formationwafers are placed above and below the particulates in the test cell. Thesystem is then shut in and placed under a pressure that is approximatelyequal to the pressure expected in the formation in which theparticulates are expected to be placed. The temperature may bemaintained at a temperature that is approximately equal to the formationtemperature where the particulates are expected to be placed. Forexample, the system may be placed under simulated formation pressure ofabout 9000 psi and temperature of about 250° F. These conditions arethen maintained for about 28 days.

Upon completion of the stress/temperature-promoted diagenesis test, thetest cell is disassembled and the particulate matrix removed fortesting. Changes in the mechanical properties of the particulates areobtained using particulates tested using the stress/temperature-promoteddiagenesis test. The analysis utilizes a Weibull statistical analysisprocedure based on a plurality of particulate crush samples, asdiscussed above. A single analysis includes a statistically significantnumber of samples, which may be between about 20 and about 40 samples,e.g., approximately 30 crushed samples of individual particles. However,in some instances, the sample size may vary such that the actual numberof samples is smaller or larger in order to obtain a statisticallysignificant number of samples. The characteristic strength changes inthe particulates may then be determined. By comparing the characteristicstrength of the particulates prior to exposure to the simulatedformation fluid with the characteristic strength of the particulatesafter exposure to the simulated formation fluid, a retained strengthvalue is calculated from the equation:

$\sigma_{0{retained}} = ( \frac{\sigma_{0{exposed}}}{\sigma_{0{unexposed}}} )$where, σ_(0 exposed) is the characteristic strength of the particlesafter exposure to the simulated formation fluid, and σ_(0 unexposed) isthe characteristic strength of the particles prior to exposure.

Similarly, the retained permeability value of the particulate pack isdefined to be measured by the temperature-promoted diagenesis test. Inthe temperature-promoted diagenesis test procedure, an initialpermeability measurement is made of a particulate pack while theparticulate pack is at room temperature. Deionized water is then heatedto a test temperature of approximately 500° F. by passing it through aheat exchanger coil. Lower test temperatures may also be used dependingon the specific particulate material and coating used. For example, oneof ordinary skill in the art may determine that a lower test temperatureis required in order to avoid thermal decomposition of the particulates,the diffusion barrier, or the filler material. Simulated formation fluidis formed by passing the deionized water through multiple packs ofcrushed formation material arranged in series. The number of formationpacks required for the test may vary such that the simulated formationfluid leaving the last pack is in equilibrium with the crushed formationmaterial at the flow rate used during the test of approximately 1milliliter per minute. The typical number of formation packs isgenerally between about 2 and about 5. Crushed formation material isscreened and an approximately 8/35 mesh fraction is used in theformation packs. The formation material is obtained by crushing a corewithdrawn from a specific well during drilling or from dill cuttingsobtained while a well is being drilled through a zone of interest.

The simulated formation fluid is then directed to a column containing aparticulate pack. The temperature in the particulate pack is maintainedat a temperature of about 500° F. A lower test temperature may be useddepending on the specific particulate material and coating materialused. For example, one of ordinary skill in the art may determine that alower test temperature is required in order to avoid thermaldecomposition of the particulates, the diffusion barrier, or the filler.A flow rate of simulated formation fluid is maintained at approximately1 milliliter per minute during the test. The flow test is maintained forabout 30 days. After this time, permeability of the particulate pack ismeasured prior to disassembly and after the particulate pack has beenallowed to cool to room temperature, allowing for a retainedpermeability to be calculated from the equation:

${Permeability}_{retained} = ( \frac{{Permeability}_{exposed}}{{Permeability}_{unexposed}} )$where, Permeability_(exposed) is the permeability of the particles afterexposure to the simulated formation fluid, and Permeability_(unexposed)is Permeability the permeability of the particles prior to exposure.

Particulates prepared and tested according to the methods of the currentinvention using the characteristic conditions of the embodiment mayexhibit a retained strength value of greater than about 20%.Alternatively, the particulates may exhibit a retained strength value ofgreater than about 60%. In still another embodiment, the particulatesmay exhibit a retained strength value of greater than about 80%. In yetanother embodiment, the particulates may exhibit a retained strengthvalue of greater than about 90%. In an embodiment, the particulates usedto form a pack may be characterized by a retained permeability value ofat least about 40%. In another embodiment, the particulates may becharacterized by a retained permeability of at least about 60%. In stillanother embodiment, the particulates may be characterized by a retainedpermeability of at least about 80%. In some embodiments, the retainedpermeability may be at least about 99%.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. While compositions and methods aredescribed in terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps. Allnumbers and ranges disclosed above may vary by some amount. Whenever anumerical range with a lower limit and an upper limit is disclosed, anynumber and any included range falling within the range is specificallydisclosed. In particular, every range of values (of the form, “fromabout a to about b,” or, equivalently, “from approximately a to b,” or,equivalently, “from approximately a-b”) disclosed herein is to beunderstood to set forth every number and range encompassed within thebroader range of values. Also, the terms in the claims have their plain,ordinary meaning unless otherwise explicitly and clearly defined by thepatentee. Moreover, the indefinite articles “a” or “an,” as used in theclaims, are defined herein to mean one or more than one of the elementthat it introduces. If there is any conflict in the usages of a word orterm in this specification and one or more patent or other documentsthat may be incorporated herein by reference, the definitions that areconsistent with this specification should be adopted.

What is claimed is:
 1. A composition comprising: a carrier fluid; aplurality of particulates, at least some of the particulates having acoating applied thereto that at least partially covers the particulatesand impedes the intrusion of water into the particulates; and a silicascale control additive in the carrier fluid at a concentration betweenabout 1 and 1000 parts per million by weight of the carrier fluid,wherein the silica scale control additive is capable of suppressingsilica scale build-up proximate the plurality of particulates; whereinthe coating is less than about 10 micrometers thick and comprises atleast one hydrophobic substance selected from the group consisting of: areaction product of a compound having a reactive silyl group, a siliconoxide anchor layer upon which a chloroalkylsilane is deposited, a hybridorgano-silicon oxide anchor layer upon which a chloroalkylsilane isdeposited, a silicone, a siloxane, a diffusion barrier comprising atrimethylsilyl functional group, an organosiloxane, an organosilane, afluoro-organosiloxane, a fluoro-organosilane, a polysiloxane, anorganomodified polysiloxane, a di-betaine polysiloxane, a di-quaternarypolysiloxane, a polymer of a fluoroalkyl-group containing silanecompound, a dimer of a fluoroalkyl-group containing silane compound, atrimer of a fluoroalkyl-group containing silane compound, a polyamide, asilyl-modified polyamide, and copolymerized polyvinylidene chloride. 2.The composition of claim 1, wherein the silica scale control additivecomprises at least one substance selected from the group consisting of:a polyaminoamide dendrimer, a polyethyleneimine, a carboxymethylinulin,a polyacrylate, a polyallylamine, a copolymer of polyacrylamide, apolyallyldimethylammonium chloride, and any combination thereof.
 3. Thecomposition of claim 1, wherein the plurality of particulates compriseat least one substance selected from the group consisting of a sand, asintered bauxite, a silica alumina, a glass bead, a bauxite, a fumedsilica, a ceramic material, a glass material, a polymer material, apolytetrafluoroethylene material, a degradable particulate, and anycombination thereof.
 4. The composition of claim 1, wherein at leastsome of the plurality of particulates are disposed in a particulate packin a subterranean formation, the particulate pack having a retainedpermeability of about 40% or more as determined using atemperature-promoted diagenesis test using formation conditions expectedfor the subterranean formation.
 5. The composition of claim 1 whereinthe carrier fluid has a pH of greater than or equal to about 4.0 andless than or equal to about 8.0.
 6. The composition of claim 1 whereinthe carrier fluid is selected from the group consisting of an aqueousfluid, a hydrocarbon fluid, and an emulsion.